Seasonal variation in zoobenthos across habitat gradients in an alpine glacial floodplain (Val Roseg, Swiss Alps)

Floodplains of glacial streams are prominent features of alpine ecosystems, yet their ecology has been little studied. The primary goal of our study was to assess the effects of habitat stability and heterogeneity on the assemblage structure of benthic macro-invertebrates in a glacial floodplain stream in the Swiss Alps. Zoobenthic assemblages were investigated during different phases of the annual hydrograph in 3 distinct habitat types (main glacial channel, intermittently connected channels, and groundwater channels). Assemblages in the main channel exhibited high temporal variability in mean densities and were dominated by Chironomidae, Ephemeroptera, and Plecoptera. In contrast, groundwater channels displayed low temporal variability in assemblage structure, but high within-channel-type variability. Habitat stability, spatiotemporal habitat heterogeneity, and hydrological connectivity were the primary structuring agents of the habitat templet in each habitat (channel) type. The complex channel network led to a high spatial heterogeneity in macroinvertebrate abundance and assemblage composition. As a consequence, a higher biodiversity at the floodplain scale was possible because of the presence of suitable habitat patches for taxa not able to colonize the main channel. In addition, groundwater and intermittently connected channels were potential refugia for benthic macroinvertebrates during high discharge in summer when environmental conditions in the main channel were unsuitable for most taxa.